JP2024170281A - Slab heating equipment and continuous casting equipment - Google Patents

Abstract

To provide a slab heater allowed to efficiently heat up an upper corner of a slab while preventing a magnetic flux from going into a roll, and a continuous casting installation.SOLUTION: A slab heater, in a continuous casting installation having a plurality of rolls provided in a transport direction to carry slabs successively while restraining them, comprises a heating coil provided in a manner to face a side-face portion of the slab and a magnetism shielding member provided between the rolls and the heating coil in a thickness direction of the slab.SELECTED DRAWING: Figure 2

Description

The present invention relates to a slab heating device and continuous casting equipment that heats slabs that are continuously transported by multiple rolls.

In a continuous casting facility where molten metal (molten steel) is cooled in a mold and slabs are produced through a casting process, the slab is first cooled and pulled out vertically by multiple roll pairs arranged along the slab's transport direction. After that, the slab is gradually curved in the upper straightening band while changing the pulling direction, and then the slab is straightened to a straight shape in the lower straightening band and pulled out horizontally.

When the slab is straightened in the lower straightening zone, tensile stress is generated at the upper corners of the slab, and if the slab has low ductility, cracks will occur at the upper corners. In general, the ductility of steel depends on the temperature of the steel. It is known that, in particular, when the temperature of the steel is between 750 and 900°C, the ductility of the steel decreases and embrittlement progresses.

When a slab is cast in a continuous casting facility, the upper corners cool faster than other parts of the slab. The temperature of the upper corners reaches 750-900°C (hereinafter referred to as the "ductility reduction temperature"), at which the ductility of the slab decreases, when the slab passes through the lower straightening zone. As a result, cracks occur in the upper corners of the slab due to the reduction in ductility of the slab caused by this temperature and the tensile stress that occurs when the slab is straightened to a horizontal shape.

Here, in order to prevent cracks from occurring at the upper corners of the slab, a technology has been proposed in which a coil for heating the upper corners of the slab is placed upstream of the lower straightening zone to heat the upper corners. In other words, this technology heats the upper corners of the slab by induction heating using a coil before the slab reaches the lower straightening zone, thereby maintaining the temperature at the upper corners above the ductility drop temperature, at which the ductility of the slab drops.

For example, Patent Document 1 discloses a technique in which coils made of conductors are arranged on the upper surface of the slab to form a predetermined group of straight lines, and the upper corners are heated by induction heating the slab, thereby suppressing cracks in the upper corners.

Patent Document 2 discloses a technology that provides an iron core that covers the upper corners of a cast piece, and uses a coil wound around the iron core to perform induction heating on the cast piece to heat the upper corners, thereby preventing cracks in the upper corners.

JP 2012-218062 A JP 2021-87963 A

However, the technologies disclosed in Patent Documents 1 and 2 adopt a configuration in which only induction heating coils for heating the slab are arranged between multiple rolls arranged along the direction of transport of the slab. Furthermore, because the distance (pitch) between the multiple rolls arranged along the direction of transport of the slab is short, it is difficult for the induction heating coils arranged between the multiple rolls to have a length sufficient to sufficiently heat the slab. Therefore, in a configuration in which induction heating coils are arranged between multiple rolls, it is difficult to sufficiently heat the slab, and the effect of preventing cracks at the upper corners of the slab cannot be fully achieved.

In addition, when an induction heating coil is placed at each position along the direction of the slab's transport in the same position as the roll, the magnetic flux generated by the induction heating coil penetrates into the slab as well as into the roll. This causes the temperatures of both the slab and the roll to rise, and fatigue damage due to thermal deformation and thermal cycles of the roll progresses, shortening the service life of the roll. Furthermore, sparks are generated between the slab and the roll into which the magnetic flux has penetrated, causing defects in the slab and the roll. Patent Documents 1 and 2 do not disclose or suggest any solutions to these problems, so the penetration of magnetic flux into the roll due to heating of the upper corner of the slab is an issue in preventing cracks in the upper corner of the slab.

The present invention was made in consideration of the above circumstances, and its purpose is to provide a slab heating device and continuous casting equipment that prevents magnetic flux from penetrating the rolls and enables efficient heating of the upper corners of the slab.

[1] A slab heating device in a continuous casting facility in which a plurality of rolls that continuously transport a slab while restraining the slab are arranged along the transport direction of the slab, the slab heating device having a heating coil arranged to face a side portion of the slab, and a magnetic shielding member arranged between the roll and the heating coil in the thickness direction of the slab.
[2] The casting heating device described in [1], wherein the heating coil is a circuit that connects and circles two coil long side portions extending in the transport direction and two coil short side portions extending in the thickness direction of the casting in the same plane.
[3] The slab heating device according to [2], wherein the magnetic shielding member has a relative permeability of 1000 or more at a frequency of an alternating current supplied from a power supply unit to the heating coil.
[4] The slab heating device described in [3], wherein the magnetic shielding member is a plate-shaped member and the plate-shaped member is arranged so as to be perpendicular to the shortest line segment connecting the central axis of the roll and the coil long side portion of the heating coil.
[5] The slab heating device described in [4], wherein the magnetic shielding members include an upper magnetic shielding member arranged perpendicular to the shortest line segment connecting a central axis of an upper roll of the rolls and an upper coil long side portion of the coil long side portion of the heating coil, and a lower magnetic shielding member arranged perpendicular to the shortest line segment connecting a central axis of a lower roll of the rolls and a lower coil long side portion of the coil long side portion of the heating coil.
[6] The slab heating device according to [5], wherein the length of the magnetic shielding member along the width direction of the slab perpendicular to the transport direction is equal to or greater than the coil diameter of the heating coil at the coil long side portion.
[7] The slab heating device according to [3], wherein the magnetic shielding member has an arc shape or a cylindrical shape that follows the circumferential surface of the roll.
[8] The slab heating device according to [5], wherein the length of the magnetic shielding member along the conveying direction is 0.7R or more where R is the diameter of the roll.
[9] The slab heating device according to any one of [1] to [8], further comprising a carriage for adjusting the positions of the heating coil and the magnetic shielding member relative to the side portion of the slab in the width direction of the slab.
[10] A continuous casting facility comprising a slab heating device according to any one of [1] to [8] in a lower straightening zone.
[11] A continuous casting equipment having a plurality of rolls arranged along the transport direction of the slab while restraining the slab and transporting it continuously, the continuous casting equipment having a circuit that connects and rotates two long side portions of the coil extending in the transport direction and two short side portions of the coil extending in the thickness direction of the slab in the same plane, and a slab heating device having a heating coil arranged so that the circuit faces the side portion of the slab, and the material of the rolls includes a non-magnetic material.

The present invention makes it possible to prevent magnetic flux from penetrating the rolls and to efficiently heat the upper corners of the slab.

FIG. 1 is a schematic side view of an example of continuous casting equipment. FIG. 2 is a perspective schematic view showing the configuration of a roll, a slab, and a slab heating device. FIG. 2 is a schematic side view showing the configuration of a slab heating device. FIG. 2 is a schematic front view showing the configuration of a magnetic shielding member. FIG. 13 is a diagram showing the distribution of magnetic flux when a slab heating device without a magnetic shielding member is used. FIG. 13 is a diagram showing the distribution of magnetic flux when a slab heating device having a magnetic shielding member is used. FIG. 11 is a side view showing a schematic configuration of a magnetic shielding member in a slab heating device according to a second embodiment. FIG. 11 is a side view showing a schematic configuration of a magnetic shielding member in a slab heating device according to a third embodiment. FIG. 13 is a side view showing a schematic configuration of a magnetic shielding member in a slab heating device according to a fourth embodiment. FIG. 13 is a schematic front view showing the configuration of a slab heating device according to a fifth embodiment. FIG. 13 is a diagram showing the results of temperature histories of a slab and a roll when no magnetic shielding member is used. FIG. 13 is a diagram showing the results of temperature history of a slab and a roll when a magnetic shielding member is used. FIG. 13 is a diagram showing the results of temperature history of a slab and a roll when a roll containing a non-magnetic material is used. FIG. 13 is a diagram showing the results of the temperature history of the slab and roll when a magnetic shielding member divided in the conveying direction is used. FIG. 13 is a diagram showing the results of temperature history of a slab and a roll when a magnetic shielding member having an arc shape is used.

First Embodiment
Hereinafter, a first embodiment of the present invention will be described in detail. FIG. 1 shows a schematic side view of an example of a continuous casting equipment 10. The continuous casting equipment 10 has a tundish 1, a mold 2, rolls 3, and a slab heating device 7. The tundish 1 has an immersion nozzle 1a. The rolls 3 are arranged from the upstream side to the downstream side in the transport direction D of the slab S. The rolls 3 sandwich the slab S between a plurality of pairs of rolls 3 at each position in the transport direction D of the slab S, and transport the slab S along the transport direction D. That is, the continuous casting equipment 10 has a plurality of rolls 3 arranged along the transport direction D of the slab S, which continuously transport the slab S while restraining it.

As shown in FIG. 1, the tundish 1 stores molten steel T before casting. The submerged nozzle 1a injects the molten steel T from the bottom of the tundish 1 into the mold 2. After being cooled in the mold 2, the molten steel T is transported along the vertical transport direction E by multiple rolls 3 and cooled in the cooling zone 4 to become a slab S with a plate thickness of 200 to 300 mm and a width of 1 to 2 m. The slab S is then transported along the curved transport direction F by the rolls 3 and curved in the upper straightening zone 5. The slab S is then transported along the horizontal transport direction G by the rolls 3 and straightened to a straight shape in the lower straightening zone 6.

In the upper straightening band 5, the temperature of the slab S is about 1000°C in the widthwise center and about 900°C at the upper corners. On the other hand, in the lower straightening band 6, the temperature of the slab S drops to about 750°C at the upper corners. In other words, the temperature of the slab S reaches the ductility reduction temperature in the lower straightening band 6. For this reason, when the slab S that has reached the ductility reduction temperature in the lower straightening band 6 is straightened into a straight shape, cracks occur due to the tensile stress generated at the upper corners of the slab S.

In the present invention, therefore, as shown in FIG. 1, a slab heating device 7 is provided in the lower straightening zone 6. Specifically, the slab heating device 7 is provided from the upstream position of the lower straightening zone 6 to the downstream position of the lower straightening zone 6. Then, for the slab S that is straightened to a straight shape in the lower straightening zone 6, the temperature of the upper corner is compensated so as not to reach the ductility reduction temperature.

Next, the configuration of the slab heating device 7 will be described with reference to FIG. 2. FIG. 2 is a perspective schematic diagram showing the configuration of the rolls 3, the slab S, and the slab heating device 7. As shown in FIG. 2, the slab heating device 7 is provided between a pair of rolls 3 (upper roll 3a and lower roll 3b) near the side portion B of the slab S. The slab heating device 7 has a heating coil 7a and a magnetic shielding member 7h. The heating coil 7a generates magnetism around it based on an alternating current supplied from a power source, and heats the surrounding structure (upper corner portion C of the slab S) by induction heating.

Here, the detailed configuration of the slab heating device 7 will be described with reference to FIG. 3. FIG. 3 is a schematic side view showing the configuration of the slab heating device 7. As shown in FIG. 3, the heating coil 7a of the slab heating device 7 has a coil long side portion 7b and a coil short side portion 7e. The coil long side portion 7b has an upper coil long side portion 7c and a lower coil long side portion 7d. In other words, the coil long side portion 7b has two coil long sides extending in the transport direction D of the slab S. In addition, the coil short side portion 7e has an upstream coil short side portion 7f and a downstream coil short side portion 7g. In other words, the coil short side portion 7e has two coil short sides extending in the thickness direction H of the slab S.

In other words, the heating coil 7a is a circuit that connects and circles two long coil sides that extend in the slab transport direction D and two short coil sides that extend in the slab thickness direction H on the same plane, and is arranged so that the circuit faces the side portion B of the slab S.

The length of the coil long side 7b (upper coil long side 7c and lower coil long side 7d) is preferably 1500 mm or more. This is because, in order to prevent the temperature at the upper corner C of the slab S from dropping to the ductility drop temperature throughout the entire lower straightening band 6 (see Figure 1), a preheat zone of 500 mm or more in length is provided upstream of the lower straightening band 6, and a heat retention zone of 1000 mm or more in length is required throughout the entire lower straightening band 6.

When it is difficult to sufficiently heat the upper corner portion C using a single circuit formed by a single coil for the heating coil 7a, multiple circuits based on multiple coils may be created and the multiple circuits may be arranged in sequence along the transport direction D of the slab S to divide the heating area of the upper corner portion C into multiple parts for heating. In this case, it is preferable that the length of the coil long side portion 7b (upper coil long side portion 7c and lower coil long side portion 7d) of the multiple divided heating coils 7a is 500 mm or more. This is because if the coil long side portion 7b is shorter than the coil short side portion 7e, the induced currents will cancel each other out between the coil short side portions 7e of the adjacent coils, reducing the heating effect of the upper corner portion C.

The length of the coil short side 7e (upstream coil short side 7f and downstream coil short side 7g) is preferably 125 mm or more and less than the thickness L of the slab S. If the length of the coil short side 7e is less than 125 mm, the induced currents will cancel each other out between the coil long side 7b of adjacent coils, reducing the heating effect of the slab S. In addition, if the length of the coil short side 7e is greater than or equal to the thickness L of the slab S, the coil long side 7b will interfere with the roll 3.

Even if there is a difference of about 10 mm in the distance between the upper coil long side portion 7c and the side portion B of the slab S, and the distance between the lower coil long side portion 7d and the side portion B of the slab S, the effect of the present invention is small. In addition, the configuration of the coil short side portion 7e (upstream coil short side portion 7f and downstream coil short side portion 7g) is not limited as long as it connects the coil long side portion 7b (upper coil long side portion 7c and lower coil long side portion 7d) as a circuit.

The heating coil 7a may be wound once or more as long as it is configured as a circuit in which the long side 7b and the short side 7e of the coil are connected by a conductor connected to a power source. The material of the heating coil 7a may be a conductor such as copper. The conductor constituting the heating coil 7a may be a hollow member, and cooling water may be circulated through the hollow area to cool the conductor. The diameter of the conductor constituting the heating coil 7a is preferably 3 mm or more. This is because increasing the diameter of the conductor reduces the resistance value of the heating coil 7a and prevents melting due to heat generation of the heating coil 7a.

The heating coil 7a may be connected to a power supply unit that supplies alternating current. The output of the power supply unit that supplies alternating current to the heating coil 7a is preferably 300 to 1000 kW. The alternating current supplied to the heating coil 7a is preferably a current (effective value) of 10 to 30 kA. If the output and current (effective value) of the power supply unit are low, the upper corner portion C of the cast piece S cannot be sufficiently heated, and if the output and current (effective value) of the power supply unit are high, there is a risk that the upper corner portion C will melt.

The alternating current supplied to the heating coil 7a preferably has a frequency of 1 to 10 kHz. If the frequency is less than 1 kHz, the entire side portion B of the slab S is heated, but it is difficult to heat the upper corner portion C to a temperature exceeding the ductility reduction temperature. If the frequency exceeds 10 kHz, only the very outer surface layer of the upper corner portion C is heated locally, making it difficult to heat the entire upper corner portion C uniformly.

The magnetic shielding member 7h is provided between the roll 3 and the heating coil 7a in the thickness direction H of the cast slab S. The magnetic shielding member 7h has an upper magnetic shielding member 7i and a lower magnetic shielding member 7j. It is preferable that the magnetic shielding member 7h has a relative permeability of 1000 or more at the frequency of the alternating current supplied from the power supply unit to the heating coil 7a, and a thickness of 1 mm or more and 10 mm or less.

Relative magnetic permeability is a parameter that indicates the degree of magnetic permeability when a material is placed in a magnetic field; the higher the value, the less magnetic permeability there is. For this reason, if the relative magnetic permeability of the magnetic shielding member 7h is low, it is necessary to increase the thickness of the magnetic shielding member 7h in order to prevent the magnetic field generated in the heating coil 7a from passing through to the roll 3. However, in this case, as the thickness of the magnetic shielding member 7h increases, the distance between the coil long side 7b (upper coil long side 7c and lower coil long side 7d) of the heating coil 7a and the upper corner portion C of the cast slab S increases, making it difficult to efficiently heat the upper corner portion C.

On the other hand, if the relative permeability of the magnetic shielding member 7h is increased to reduce the thickness of the magnetic shielding member 7h, it is possible to prevent the magnetic field generated by the heating coil 7a from penetrating the roll 3, but it is difficult to ensure the strength of the member.

For this reason, the magnetic shielding member 7h has a thickness of 1 mm to 10 mm, which is capable of preventing deformation due to the effects of heating, and by having a relative magnetic permeability of 1000 or more based on this thickness, it is possible to prevent the magnetic field generated in the heating coil 7a from penetrating (magnetic flux leakage) into the roll 3. In addition, examples of materials for the magnetic shielding member 7h include iron-based materials, ferrite, amorphous, permalloy, sendust, etc., but the material is not limited as long as it can prevent magnetic penetration. The magnetic shielding member 7h may be configured as a hollow member, and cooling water that can cool the magnetic shielding member 7h may be circulated in the hollow area.

The magnetic shielding member 7h is a plate-shaped member and is arranged so that the plate-shaped member is perpendicular to the shortest line segment N connecting the central axis P of the roll 3 and the coil long side portion 7b. Specifically, in this embodiment, the magnetic shielding member 7h has an upper magnetic shielding member 7i arranged so as to be perpendicular to the shortest line segment N connecting the central axis P of the upper roll 3a in the roll 3 and the upper coil long side portion 7c in the coil long side portion 7b, and a lower magnetic shielding member 7j arranged so as to be perpendicular to the shortest line segment N connecting the central axis P of the lower roll 3b in the roll 3 and the lower coil long side portion 7d in the coil long side portion 7b.

By arranging the magnetic shielding member 7h, which is a plate-shaped member, so that it is perpendicular to the shortest line segment N between the central axis P of the roll 3 and the coil long side portion 7b (upper coil long side portion 7c and lower coil long side portion 7d), it is possible to more efficiently prevent the magnetic field emitted from the upper coil long side portion 7c and lower coil long side portion 7d of the heating coil 7a from penetrating into the roll 3 (upper roll 3a and lower roll 3b).

Next, the configuration of the magnetic shielding member 7h in the slab heating device 7 will be described with reference to FIG. 4. FIG. 4 is a schematic front view showing the configuration of the magnetic shielding member 7h in the slab heating device 7. That is, FIG. 4 shows a schematic front view of the slab heating device 7 viewed in the conveying direction D of the slab S.

As shown in FIG. 4, it is preferable that the length of the magnetic shielding member 7h along the width direction W of the slab S perpendicular to the conveying direction D is equal to or greater than the coil diameter U of the heating coil 7a at the coil long side portion 7b (upper coil long side portion 7c and lower coil long side portion 7d). From the viewpoint of preventing heating of the roll 3, it is more preferable that the length of the magnetic shielding member 7h along the width direction W of the slab S is equal to or greater than 50 mm.

In addition, in order to avoid contact due to meandering of the slab S during transportation and to promote heating of the slab S, the magnetic shielding member 7h may be spaced from the slab S in the width direction W by the same distance as the distance between the coil long side portion 7b and the side portion B of the slab S (hereinafter referred to as "distance CS"). In addition, in order to avoid contact with the coil long side portion 7b due to meandering of the slab S, it is preferable that the distance CS is 25 mm or more. In addition, if the distance CS is too large, the heating effect of the slab S decreases. In addition, since it also induces melting of the coil due to an increase in the current (effective value) of the alternating current aimed at improving the heating efficiency, the distance CS is preferably less than 50 mm.

From the viewpoint of providing a magnetic shielding member 7h, the distance between the coil long side portion 7b of the heating coil 7a and the roll 3 (hereinafter referred to as "distance CR") is preferably 1 mm or more. Furthermore, if the distance between the coil long side portion 7b and the roll 3 is too large, the distance between the coil long side portion 7b and the upper corner portion C also becomes large, and the efficiency of heating the upper corner portion C decreases. In addition, it also induces melting of the coil due to an increase in the current (effective value) of the alternating current intended to improve the heating efficiency. For this reason, it is preferable that the distance CR is less than 30 mm.

Next, the effects based on the above-mentioned configuration will be explained using Figures 5 and 6. Figure 5 is a diagram showing the distribution of magnetic flux when a slab heating device 7 without a magnetic shielding member 7h is used. Figure 6 is a diagram showing the distribution of magnetic flux when a slab heating device 7 with a magnetic shielding member 7h is used.

As shown in FIG. 5, when an AC current is supplied to the heating coil 7a in a slab heating device 7 that does not have a magnetic shielding member 7h, magnetic flux M is generated and penetrates the roll 3. On the other hand, when an AC current is supplied to the heating coil 7a in a slab heating device 7 that has a magnetic shielding member 7h, magnetic flux M is generated and is attracted to the inside of the magnetic shielding member 7h as shown in FIG. 6. The direction of the magnetic flux M attracted to the inside of the magnetic shielding member 7h is parallel to the surface of the magnetic shielding member 7h that extends toward the width direction W of the slab S, and the magnetic flux M is prevented from penetrating the roll 3. Furthermore, the magnetic flux M that is parallel to the surface of the magnetic shielding member 7h efficiently penetrates the side portion B of the slab S and the upper corner portion C while maintaining that direction. Therefore, by having the magnetic shielding member 7h, efficient heating of the upper corner portion C of the slab S is possible, and the penetration of magnetism into the roll 3 can be prevented.

In this embodiment, as shown in FIG. 3, the magnetic shielding member 7h is described as having an upper magnetic shielding member 7i and a lower magnetic shielding member 7j. However, the magnetic shielding member 7h may be configured only with the upper magnetic shielding member 7i without providing the lower magnetic shielding member 7j. In this case, providing at least the upper magnetic shielding member 7i makes it possible to efficiently heat the upper corner portion C of the cast piece S and prevents magnetism from penetrating into the upper roll 3a.

In addition to using the magnetic shielding member 7h, the material of the roll 3 may also include a non-magnetic material. By including a non-magnetic material in the material of the roll 3, it is possible to more effectively prevent magnetism from penetrating the roll 3 compared to the case where only the magnetic shielding member 7h is used. This provides an excellent effect in preventing heating of the roll 3 and damage to the roll 3. Examples of materials that make the roll 3 non-magnetic include ceramic materials and austenitic stainless steel.

Second Embodiment
Next, a second embodiment of the present invention will be described. Fig. 7 shows a schematic configuration of a magnetic shielding member 72b in a slab heating device 72 of the second embodiment. Fig. 7 shows an example of a configuration in which the magnetic shielding member 72b is divided in the transport direction D of the slab S. The second embodiment has the same configuration as the first embodiment, except for the configuration in which the magnetic shielding member 72b is divided.

As shown in FIG. 7, by dividing the magnetic shielding member 72b in the conveying direction D of the slab S and arranging the magnetic shielding member 72b only between the roll 3 and the heating coil 72a (including the coil long side portion 72c and the coil long side portion 72d), it is possible to prevent the magnetic flux from penetrating the roll 3 and to simplify the configuration of the magnetic shielding member 72b. Furthermore, by not providing the magnetic shielding member 72b in the same position as the position where the roll 3 is not arranged in the conveying direction D, the magnetic flux generated from the heating coil 72a can be made to act on the upper corner portion C of the slab S. Therefore, the upper corner portion C can be efficiently heated. From the viewpoint of preventing the magnetic flux from penetrating the roll 3, it is preferable that the length of the magnetic shielding member 72b in the conveying direction D is 0.7R or more with respect to the roll diameter R of the roll 3.

Third Embodiment
Next, a third embodiment of the present invention will be described. Fig. 8 shows a schematic configuration of a magnetic shielding member 73b in a slab heating device 73 of the third embodiment. Fig. 8 shows an example of a configuration in which the length of the magnetic shielding member 73b in the width direction W of the slab S is approximately the same as the coil diameter of the heating coil 73a. The third embodiment has the same configuration as the first embodiment, except for the configuration in which the length of the magnetic shielding member 73b in the width direction W of the slab S is approximately the same as the coil diameter of the heating coil 73a.

As shown in FIG. 8, by making the length of the magnetic shielding member 73b approximately the same as the coil diameter of the heating coil 73a in the width direction W of the cast slab S, it is possible to prevent magnetism from penetrating the roll 3 and also to simplify the configuration of the magnetic shielding member 73b.

Fourth Embodiment
Next, a fourth embodiment of the present invention will be described. FIG. 9 shows a schematic configuration of a magnetic shielding member 74c and a magnetic shielding member 74d in a slab heating device 74 of the fourth embodiment. FIG. 9(a) shows an example of a configuration in which the magnetic shielding member 74c is formed in an arc shape along the circumferential surface K of the roll 3. FIG. 9(b) shows an example of a configuration in which the magnetic shielding member 74d is formed in a cylindrical shape along the circumferential surface K of the roll 3. In the fourth embodiment, except for the configuration in which the magnetic shielding member 74c and the magnetic shielding member 74d are formed in an arc shape or a cylindrical shape, the configuration is the same as that of the first embodiment. The heating coil 74a in FIG. 9(a) includes a coil long side portion 74e and a coil long side portion 74f. The heating coil 74b in FIG. 9(b) includes a coil long side portion 74g and a coil long side portion 74h.

As shown in FIG. 9, by forming the magnetic shielding members 74c and 74d in an arc shape or a cylindrical shape along the peripheral surface K of the roll 3 in the conveying direction D of the cast slab S, the magnetic shielding members 74c and 74d can be provided in a position close to the upper corner portion C of the cast slab S while more reliably preventing the magnetic flux from penetrating the roll 3. With this configuration, the magnetic flux concentrated in the magnetic shielding members 74c and 74d can be concentrated in the upper corner portion C, and the upper corner portion C can be efficiently heated. From the viewpoint of preventing the magnetic flux from penetrating the roll 3, when the magnetic shielding members 74c are configured in an arc shape as shown, it is preferable that the length of the chord of the arc is 0.7R or more with respect to the roll diameter R of the roll 3.

Fifth Embodiment
Next, a fifth embodiment of the present invention will be described. Fig. 10 shows a schematic configuration of a slab heating device 75 according to the fifth embodiment. Fig. 10 shows an example of a configuration of the slab heating device 75 including a carriage 75e and a distance measuring device 75f. The fifth embodiment has the same configuration as the first embodiment, except for the configuration in which the slab heating device 75 includes the carriage 75e and the distance measuring device 75f.

As shown in FIG. 10, the slab heating device 75 has a heating coil 75a, a magnetic shielding member 75b, a conductive rod 75c, a power supply unit 75d, a carriage 75e, a distance measuring device 75f, and a drive unit 75g. The power supply unit 75d supplies AC current to the conductive rod 75c. The conductive rod 75c supplies the AC current supplied from the power supply unit 75d to the heating coil 75a. The heating coil 75a heats the upper corner portion C of the slab S with the AC current supplied via the conductive rod 75c.

The distance measuring device 75f may be a laser distance meter. The distance measuring device 75f may measure the distance between the heating coil 75a and the magnetic shielding member 75b and the side portion B of the cast piece S. The cart 75e may be controlled to adjust the distance between the heating coil 75a and the magnetic shielding member 75b and the side portion B of the cast piece S based on the distance measurement value measured by the distance measuring device 75f.

Furthermore, the distance measuring device 75f may measure the distance between the upper roll 3a and the lower roll 3b. The driving unit 75g may be controlled to adjust the distance between the upper heating coil 75a and the magnetic shielding member 75b and the lower heating coil 75a and the magnetic shielding member 75b based on the distance measurement value measured by the distance measuring device 75f.

That is, in this embodiment, the position of the heating coil 75a and the magnetic shielding member 75b relative to the side portion B of the slab S may be adjusted by the cart 75e in the width direction W of the slab S. In addition, since the distance between the upper heating coil 75a and the magnetic shielding member 75b and the lower heating coil 75a and the magnetic shielding member 75b can be adjusted, heating of the upper corner portion C can be reliably performed regardless of the size of the slab S.

Sixth Embodiment
Next, a sixth embodiment of the present invention will be described. In the sixth embodiment, the material of the roll 3 may be a non-magnetic material instead of using a magnetic shielding member. The sixth embodiment has the same configuration as the first embodiment, except that the material of the roll 3 is a non-magnetic material without using a magnetic shielding member.

By using a non-magnetic material for the roll 3, the intrusion of magnetism can be prevented more effectively than when only a magnetic shielding member is used. This prevents the roll 3 from heating up, and is effective in preventing damage to the roll 3. Examples of materials that can be used to make the roll 3 non-magnetic include ceramic materials and austenitic stainless steel.

Although the configurations of the first to sixth embodiments have been described above, in the present invention, the configurations of the respective embodiments can be combined as long as the effect of preventing the intrusion of magnetic flux M into the roll 3 and enabling efficient heating of the upper corner portion C of the slab S is achieved. For example, the magnetic shielding member 74c may be configured to have an arc shape along the peripheral surface K of the roll 3 in the conveying direction D (see FIG. 9(a)), and the length of the magnetic shielding member 7h in the width direction W may be configured to be equal to or longer than the coil diameter U of the heating coil 7a (see FIG. 4), and further the material of the roll 3 may include a non-magnetic material.

Next, the results of implementing the casting heating device and continuous casting equipment according to the present invention by applying them to the process of casting casting S will be described. The comparative example and invention example 1 described below are implementation results conducted with a focus on the configuration in the first embodiment. Invention example 2 is an implementation result conducted with a focus on the configuration in the sixth embodiment. Invention example 3 is an implementation result conducted with a focus on the configuration in the second embodiment. Invention example 4 is an implementation result conducted with a focus on the configuration in the fourth embodiment.

In the example, the cross-sectional size of the cast piece S was a width of 1200 mm and a thickness of 300 mm, and ordinary carbon steel was used as the material for the cast piece S. In the casting process, the initial temperature of the corners of the cast piece S was 750°C, and the conveying speed of the cast piece S in the conveying direction D was 0.9 m/min. The length of the long side of the heating coil was 1500 mm, and the length of the short side of the coil was 250 mm. The magnetic shielding member had a relative magnetic permeability of 1000 and a thickness of 1 mm. The alternating current supplied to the heating coil had a frequency of 10 kHz and a current (effective value) of 10 kA.

As a comparative example, FIG. 11 shows the results of the temperature history from the heating start point of the slab S and roll 3 when the magnetic shielding member 7h was not used. FIG. 11(a) is a perspective schematic diagram showing the configuration of the slab S, roll 3, and heating coil 7a. FIG. 11(b) is a front schematic diagram showing the configuration of the slab S, roll 3, and coil long side portion 7b in the width direction W. FIG. 11(c) is a diagram showing the results of the temperature history of the upper corner portion (X) of the slab S and a position (Y) near the coil long side portion 7b on the roll 3. The roll 3 in the comparative example was a normal roll without containing a non-magnetic material.

As shown in Figure 11 (c), the upper corner (X) of the slab S was heated to a temperature of only about 900°C, which was the ductility-reducing temperature when it passed through the lower straightening zone, causing cracks at the upper corner (X). In addition, the heated temperature at a position (Y) near the coil long side 7b on the roll 3 reached about 850°C, causing damage due to thermal deformation. Furthermore, a spark occurred between the coil long side 7b and the roll 3, damaging the slab S as well.

Figure 12 shows the results of the temperature history from the heating start point of the slab S and roll 3 when the magnetic shielding member 7h is used as Example 1 of the invention. Figure 12(a) is a perspective schematic diagram showing the configuration of the slab S, roll 3, magnetic shielding member 7h, and heating coil 7a. Figure 12(b) is a front schematic diagram showing the configuration of the slab S, roll 3, magnetic shielding member 7h, and coil long side portion 7b in the width direction W. Figure 12(c) is a diagram showing the results of the temperature history of the upper corner portion (X) of the slab S and the position (Y) near the coil long side portion 7b on the roll 3. The roll 3 in Example 1 of the invention is a normal roll that does not contain a non-magnetic material.

As shown in Figure 12 (c), the upper corner portion (X) of the slab S was heated to a temperature of about 1000°C, exceeding the ductility reduction temperature, when it passed through the lower straightening zone, so no cracks were generated at the upper corner portion (X). In addition, the heated temperature at the position (Y) near the coil long side portion 7b on the roll 3 was only about 200°C, preventing damage due to thermal deformation.

In Example 2, instead of using the magnetic shielding member 7h, a roll 8 made of a non-magnetic austenitic stainless steel material (SUS304) is used, and the results of the temperature history from the heating start point of the slab S and roll 8 in this case are shown in Figure 13. Figure 13(a) is a perspective schematic diagram showing the configuration of the slab S, roll 8, and heating coil 7a. Figure 13(b) is a front schematic diagram showing the configuration of the slab S, roll 8, and coil long side portion 7b in the width direction W. Figure 13(c) is a diagram showing the results of the temperature history of the upper corner portion (X) of the slab S and the position (Y) near the coil long side portion 7b on the roll 8.

As shown in Figure 13 (c), the upper corner portion (X) of the slab S was heated to a temperature of about 1000°C, exceeding the ductility reduction temperature, when it passed through the lower straightening zone, so no cracks were generated at the upper corner portion (X). In addition, the heated temperature at the position (Y) near the coil long side portion 7b on the roll 8 remained at about 140°C, preventing damage due to thermal deformation.

As an example 3 of the invention, a magnetic shielding member 72b divided in the conveying direction D of the slab S was used, and the results of the temperature history from the heating start point of the slab S and the roll 3 in this case are shown in Figure 14. Figure 14(a) is a perspective schematic diagram showing the configuration of the slab S, the roll 3, the magnetic shielding member 72b, and the heating coil 72a. Figure 14(b) is a front schematic diagram showing the configuration of the slab S, the roll 3, the magnetic shielding member 72b, and the coil long side portion 72c and the coil long side portion 72d in the width direction W. Figure 14(c) is a diagram showing the results of the temperature history of the upper corner portion (X) of the slab S and the position (Y) near the coil long side portion 72c on the roll 3. The roll 3 in the example 3 of the invention was a normal roll without including a non-magnetic material.

As shown in FIG. 14(c), the heating temperature of the slab S at the upper corners (X) could be increased at an earlier stage than in a configuration in which the magnetic shielding member was not divided across the conveying direction D (see Example 1). As a result, the slab S passed through the lower straightening zone at a temperature above the ductility reduction temperature, and no cracks were generated at the upper corners (X). In addition, the temperature at the position (Y) near the coil long side 72c on the roll 3 could be maintained at the same level as in a configuration in which the magnetic shielding member was not divided across the conveying direction D (see Example 1), preventing damage due to thermal deformation.

As an example 4 of the invention, a magnetic shielding member 74c in the shape of an arc along the circumferential surface of the roll 3 in the conveying direction D of the slab S is used, and the results of the temperature history from the heating start point of the slab S and the roll 3 in this case are shown in Figure 15. Figure 15 (a) is a perspective schematic diagram showing the configuration of the slab S, the roll 3, the magnetic shielding member 74c, and the heating coil 74a. Figure 15 (b) is a front schematic diagram showing the configuration of the slab S, the roll 3, the magnetic shielding member 74c, the coil long side portion 74e, and the coil long side portion 74f in the width direction W. Figure 15 (c) is a diagram showing the results of the temperature history of the upper corner portion (X) of the slab S and the position (Y) near the coil long side portion 74e on the roll 3. The roll 3 in the example 4 of the invention is a normal roll without including a non-magnetic material.

As shown in FIG. 15(c), the heating temperature of the slab S at the upper corner (X) could be increased at an earlier stage than in a configuration in which the magnetic shielding member was not divided across the conveying direction D (see Example 1). As a result, the slab passed through the lower straightening zone at a temperature above the ductility reduction temperature, and no cracks were generated at the upper corner (X). In addition, the temperature near the coil long side 74e of the roll 3 at the position (Y) could be maintained at the same level as in a configuration in which the magnetic shielding member was not divided across the conveying direction D (see Example 1), preventing damage due to thermal deformation.

REFERENCE SIGNS LIST 1 Tundish 2 Mold 3, 8 Rolls 3a Upper roll 3b Lower roll 4 Cooling zone 5 Upper straightening zone 6 Lower straightening zone 7 Strand heating device 7a Heating coil 7b Coil long side 7c Upper coil long side 7d Lower coil long side 7e Coil short side 7f Upstream coil short side 7g Downstream coil short side 7h Magnetic shielding member 7i Upper magnetic shielding member 7j Lower magnetic shielding member B Side portion C Upper corner portion D Transport direction E Vertical transport direction F Curved transport direction G Horizontal transport direction H Thickness direction M Magnetic flux S Strand T Molten steel W Width direction

Claims (11)

A slab heating device in a continuous casting facility in which a plurality of rolls for continuously conveying a slab while restraining the slab are provided along a conveying direction of the slab,
a heating coil provided to face a side surface of the slab;
a magnetic shielding member provided between the roll and the heating coil in the thickness direction of the slab;
A slab heating device comprising: The slab heating device according to claim 1, wherein the heating coil is a circuit that connects and circles two coil long sides that extend in the transport direction and two coil short sides that extend in the thickness direction of the slab on the same plane. The casting heating device according to claim 2, wherein the magnetic shielding member has a relative magnetic permeability of 1000 or more at the frequency of the alternating current supplied from the power supply unit to the heating coil. The casting heating device according to claim 3, wherein the magnetic shielding member is a plate-shaped member and is arranged so as to be perpendicular to the shortest line segment connecting the central axis of the roll and the long side of the heating coil. The casting heating device according to claim 4, wherein the magnetic shielding members include an upper magnetic shielding member that is arranged so as to be perpendicular to the shortest line segment connecting the central axis of the upper roll of the roll and the upper coil long side of the coil long side of the heating coil, and a lower magnetic shielding member that is arranged so as to be perpendicular to the shortest line segment connecting the central axis of the lower roll of the roll and the lower coil long side of the coil long side of the heating coil. The slab heating device according to claim 5, wherein the length of the magnetic shielding member along the width direction of the slab perpendicular to the transport direction is equal to or greater than the coil diameter of the heating coil at the long side of the coil. The casting heating device according to claim 3, wherein the magnetic shielding member is an arc or cylindrical shape that follows the circumferential surface of the roll. The casting heating device according to claim 5, wherein the length of the magnetic shielding member along the conveying direction is 0.7R or more with respect to the diameter R of the roll. The slab heating device according to any one of claims 1 to 8, further comprising a carriage for adjusting the position of the heating coil and the magnetic shielding member relative to the side of the slab in the width direction of the slab. A continuous casting facility in which the slab heating device according to any one of claims 1 to 8 is provided in the lower straightening zone. A continuous casting facility in which a plurality of rolls for continuously conveying a slab while restraining the slab are provided along a conveying direction of the slab,
a slab heating device having a circuit that connects and winds two coil long side portions extending in the transport direction and two coil short side portions extending in the thickness direction of the slab in the same plane, the circuit being provided so as to face a side portion of the slab;
The continuous casting equipment, wherein the roll material includes a non-magnetic material.

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